(SRI) - Swiss prosecutors have reportedly launched an investigation into money laundering allegations by Kazakh billionaire Timur Kulibayev, according to British and Kazakh media.

"The office of the attorney general of Switzerland opened a criminal investigation in September 2010 into allegations of money laundering against Timur Kulibayev, one of his associates, Arvind Tiku, and others," Bruno de Preux, a Swiss lawyer representing an unnamed group of Kazakh citizens, said in a statement.

A spokesman for the public prosecutor's office in Switzerland would not "confirm nor comment on" whether it had begun an investigation.

The investigation is reportedly focusing on $600 million held in Swiss bank accounts that was allegedly bribe money paid to Kulibayev in connection to the sale of Kazakh state-owned oil and gas assets.

Kulibayev, the son-in-law of Kazakhstan's President Nursultan Nazarbayev and one of the most influential Kazakh businessmen, has been repeatedly accused of misappropriating funds while holding high positions at the Ministry of Energy of Mineral Resources and the national oil company KazMunaiGas. Earlier this year, Kazakhstan's financial police investigated claims of corruption against Kulibayev in connection with the sale of a major Kazakh oil company to Chinese investors but dismissed the case as unfounded.

Kulibayev himself has denied any allegations of corruption.